This invention relates to cooling towers wherein heat is exchanged between water and air, and more particularly involves an improved counterflow cooling tower with heat transfer media construction and method of operation which enables the vertical dimension of the cooling tower to be reduced and improves airflow through the media.
The design of counterflow cooling towers is a well developed technology. In one style of counterflow cooling tower which is widely applied in commercial installations heat transfer media comprising a plurality of fill sheets are mounted vertically and slightly spaced so as to provide vertical air channels between adjacent sheets, and ambient air is passed upwardly while heated water is flowed downwardly on the surface of the sheets to effect heat exchange to cool the water. The fill sheets have been relatively flat parallelograms, usually rectangles, of relatively impervious material with surface embossments to keep adjacent sheets spaced apart and to distribute a film of water on each surface. Such sheets have been arrayed in a horizontal bank with the lower edges positioned horizontally and held generally parallel and even with one another at a uniform distance above a water sump or pool in the bottom of the cooling tower so as to provide a rectangular plenum for air to enter beneath the fill sheets, as shown, for example, in U.S. Pat. No. 3,132,190 to Engalitcheff Jr. Above the bank of fill sheets a water distribution network is located and balanced so as to deliver substantially uniform rates of water flow to all portions of the fill sheets; and above that an air outlet is located.
Rarely do counterflow heat exchangers depart from such an arrangement, although there has been a design for such a unit wherein a pack of multiple fill units is shaped to form a sloping bank of interconnected uniform symmetrical fill sheets arranged with the sheets perpendicular to the entering air flow, as shown in U.S. Pat. No. 3,983,190 to Norback.
It is to be understood that other types of heat transfer media may be employed in a cooling tower, such as serpentine or coiled tubing wherein another fluid is circulated, and combinations of fill sheets and tubing. The present invention is also applicable to such other heat transfer media which is referred to herein collectively as media.
While it is sometimes possible to provide for a natural air draft through such a counterflow cooling tower, it is far more common that air is propelled mechanically. This may be by either forced draft, where one or more fans drive air from one or more sides of the cooling tower into the plenum below the fill sheets, or induced draft, where one or more fans are mounted above the fill sheets and water distributor and draw air through the plenum and media. In all such instances the air enters the plenum horizontally and therein gradually turns upwardly to pass between the media.
A number of factors such as fan shrouding, the dynamics of air flow through the fan, and distance from the air inlet contribute to an uneven distribution of air flowing between the media. In the past this has usually been compensated by maximizing the vertical dimension and space within the plenum, orienting the lowermost media to be perpendicular to the initial horizontal direction of air entering the cooling tower and/or sometimes positioning control vanes within the plenum. Even so in prior cooling towers the air entering the plenum has tended to move horizontally beyond the media adjacent the air entry resulting in an area of media close to the entry way that is relatively starved for vertically moving air and a consequent reduction in efficiency. This has been particularly true of forced draft towers employing centrifugal fans which heretofore tended to thrust air with great force toward a far side of the plenum.
Moreover, it has been found that the overall height of a cooling tower is limited by practical considerations such as the need to reduce risk of wind damage, vertical structural restraints and restrictions at the location of installation (space between floors and maximum height for buildings) and the visual impact of a cooling tower respecting its surroundings. Another important factor applies to factory constructed cooling towers which are shipped from a manufacturing plant to an installation site along rail lines and roadways with vertical limits imposed by either the carrier equipment or bridges, and the like, along the route.